PROJECT SUMMARY/ABSTRACT Chimeric antigen receptor (CAR) T cells have revolutionized cancer therapies and show incredible responses in patients with relapsed or refractory B cell cancers, yet are ineffective in solid tumors. In order to work in solid tumors, CAR T cells must be able to survive the immunosuppressive tumor microenvironment (TME) and distinguish between antigens presented on tumor cells and healthy tissue. Both of these obstacles can be overcome through clever synthetic engineering of the T cell using known biological circuits. We have identified a pathway critical to the survival and function of multiple types of leukocytes and naturally turned on during activation of CD8+ T cells, however surprisingly, it is not activated in the tumor microenvironment. Here, I propose to synthetically activate this pathway in order to promote CD8+ CAR T cell cytotoxicity and on-target, on-tumor specificity. Specifically, I will first explore multiple aspects of this signaling pathway and its ability to promote CAR T cell survival and cytotoxicity under the stresses in the tumor microenvironment. As a second strategy to improve CAR-T cell specificity for solid tumors, I will engineer a construct that selectively activates a CAR in response to post-transcriptional regulation. Benefits of post-transcriptional regulation include speed of activation, and amplification of signal. By making both the post-transcriptional regulator and the target dependent on binding target cell antigens, I will functionally create an ?AND? logic gate, requiring stimulation from 2 separate antigens in order to facilitate CAR T cell killing. For both strategies I will first demonstrate their efficacy in vitro with primary mouse and human cells simulating TME conditions, and then in vivo using a syngeneic transplanted melanoma mouse model. Overall, I hypothesize that synthetic activation of this critical T cell pathway will enhance CAR-T behavior and control in the solid TME.